1. Field of the invention
The present invention relates to a welding method and a welding device which are utilized for melting and jointing members, to weld the members by applying a local heat supply such as a laser beam, etc., to surfaces of the members to be welded, while supplying a filler wire to the locally heated portion of the surfaces.
2. Description of the Related Art
A locally heating welding method using a local heat supply, such as a laser beam etc., provides a little heat input to members to be welded. This results in little welding distortion. Therefore, the locally heating welding method is utilized for butt welding and lap welding of thin steel sheets. The reason for little heat input is that the welding method enables applying the local heat supply, such as a laser beam etc., into a very small area and thereby enabling a concentration of energy of the local heat supply.
However, on the other hand, the locally heating welding method has drawbacks that an allowable bound of a deviation of the applying area of the local heat supply from a desired portion of the members to be welded is so narrow, and further, an allowable bound of a magnitude of the gap between the members is so narrow.
Consequently, e.g., in butt welding of thin steel sheets, the welding is sometimes accompanied with supplying a filler wire to enlarge the allowable bound of magnitude of the gap. However, in this case, allowable bound of the magnitude of the gap is enlarged, while a new problem of a deviation of the applying area of the local heat supply from the filler wire arises. The deviation of the applying area of the local heat supply from the filler wire results in non-uniform and non-steady melting of the filler wire causing humping of a weld bead. This humping makes it difficult to obtain a required weld strength.
To reduce occurrence of weld inferiority from humping, prior welding methods generally raise a mechanical accuracy of a filler wire supplying device and/or raise an accuracy of an optical system for the local heat supply such as a laser beam etc. Furthermore, as shown in FIGS. 8A, 8B, e.g. for melting and jointing abutting members 52, 53 to be welded, by applying a laser beam 55 to the abutting portion 54 of the members 52, 53 while supplying a filler wire 56 to the abutting portion 54, a prior welding method increases the diameter of the laser beam 55 than that of the filler wire 56 to enlarge the allowable bound of the deviation of the applying area of the laser beam 55 from the filler wire 56.
Though, such prior welding methods can not suppress essentially the occurrences of above mentioned weld inferiority, so that in general, an inferiorly welded part detecting device which detects a inferiorly welded part after welding is provided in a prior welding device to prevent supplying inferior goods to a posterior manufacturing process.
As a welding device having a inferior part detecting device detects an inferiorly welded part by inspecting a form of a weld bead after welding. A welding device which takes a picture of the form of the weld bead by an industrial television (ITV) camera is previously known in Japanese Patent Application Laid Open No. 40692/88, which welding device then inputs and processes the form of the weld bead as an image to detect inferior forms of the weld bead.
However, the above mentioned increasing of the diameter of the laser beam than that of the filler wire causes decreasing of power density of the laser beam which makes the welding device to slow down the welding speed, and further causes increasing of the width of the weld bead resulting a large welding distortion.
On the other hand, the above mentioned inspecting of the form of the weld bead enables only judgement of good or inferior forms of the weld bead after welding. Consequently, since welding conditions can not be corrected by the inspection of the form of the weld bead, the welded members having inferiorly welded portion must be scrapped, so that especially in the case of large members, costs of materials become very expensive.
Thus, it has been proposed to provide a welding method and a welding device which enable preventing occurrence of above mentioned weld inferiority by correcting welding conditions during welding instead of detecting weld inferiority after welding.
It is an object of the invention to provide a welding method and a welding device which method and device enable preventing occurrence of weld inferiority due to the relative deviation between the applying area of the laser beam and the filler wire, during melting and jointing members to weld the members by applying a local heat supply to surfaces of the members while supplying a filler wire to the locally heated portion of the surfaces, thereby decreasing scrapped inferior members and reducing costs of materials and improving weld efficiency.